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CVE PROGRAM SOURCE RECORD7.0 High

CVE-2026-52969

KVM: Reject wrapped offset in kvm_reset_dirty_gfn()

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Status
Published
Published
Updated
Assigning organization
Linux

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: Reject wrapped offset in kvm_reset_dirty_gfn() kvm_reset_dirty_gfn() guards the gfn range with if (!memslot || (offset + __fls(mask)) >= memslot->npages) return; but offset is u64 and the addition is unchecked. The check can be silently bypassed by a u64 wrap. The dirty ring backing those entries is MAP_SHARED at KVM_DIRTY_LOG_PAGE_OFFSET of the vcpu fd, so the VMM can rewrite the slot and offset fields of any entry between when the kernel pushes them and when KVM_RESET_DIRTY_RINGS consumes them. On reset, kvm_dirty_ring_reset() re-reads the values via READ_ONCE() and feeds them straight back into this check; only the flags handshake is treated as the handover, the slot/offset payload is taken on trust. Crafting two entries entry[i].offset = 0xffffffffffffffc1 entry[i+1].offset = 0 makes the coalescing loop in kvm_dirty_ring_reset() compute delta = (s64)(0 - 0xffffffffffffffc1) = 63 which falls in [0, BITS_PER_LONG), so it folds entry[i+1] into the existing mask by setting bit 63. The trailing kvm_reset_dirty_gfn() call then sees offset = 0xffffffffffffffc1 and __fls(mask) = 63; the sum is 0 in u64 and the bounds check passes. That offset propagates into kvm_arch_mmu_enable_log_dirty_pt_masked() unchanged. On the legacy MMU path -- kvm_memslots_have_rmaps() == true, i.e. shadow paging, any VM that has allocated shadow roots, or a write-tracked slot -- it reaches gfn_to_rmap(), which indexes slot->arch.rmap[0][] with a near-U64_MAX gfn. That is an out-of-bounds load of a kvm_rmap_head, followed by a conditional clear of PT_WRITABLE_MASK in whatever the loaded pointer points at. The path is reachable from any process holding /dev/kvm. Range-check offset on its own first, so the addition cannot wrap. memslot->npages is bounded well below U64_MAX, so once offset < npages holds, offset + __fls(mask) (with __fls(mask) < BITS_PER_LONG) stays in range.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Linux Linux

Default version status: unaffected

  • fb04a1eddb1a65b6588a021bdc132270d5ae48bb to < 74f1a22f7a80f03d28ad8551a2d25d563433addfaffected
  • fb04a1eddb1a65b6588a021bdc132270d5ae48bb to < 0eb281eb95b2d4eea4db1da5fe91023aecc97095affected
  • fb04a1eddb1a65b6588a021bdc132270d5ae48bb to < 01b71b930f15728aa8599478a7ce90c19dcd9fc2affected
  • fb04a1eddb1a65b6588a021bdc132270d5ae48bb to < b315b033a877b1ee6d827810b5d7bb4392ffcf8daffected
  • fb04a1eddb1a65b6588a021bdc132270d5ae48bb to < 0d419c23bb11b5c9664de777c47c1f04a235882daffected
  • fb04a1eddb1a65b6588a021bdc132270d5ae48bb to < ecf9b3ea7847fe14f34b8c41f00de1eb95c747daaffected
  • fb04a1eddb1a65b6588a021bdc132270d5ae48bb to < 577a8d3bae0531f0e5ccfac919cd8192f920a804affected

Linux Linux

Default version status: affected

  • 5.11affected
  • 0 to < 5.11unaffected
  • 5.15.209 to ≤ 5.15.*unaffected
  • 6.1.175 to ≤ 6.1.*unaffected
  • 6.6.141 to ≤ 6.6.*unaffected
  • 6.12.91 to ≤ 6.12.*unaffected
  • 6.18.33 to ≤ 6.18.*unaffected
  • 7.0.10 to ≤ 7.0.*unaffected
  • 7.1 to ≤ *unaffected

References